This invention relates to the preparation of triorganotin compounds. This invention further relates to the preparation of polymerizable triorganotin derivatives of unsaturated carboxylic acids.
Polymers derived from triorganotin derivatives of unsaturated monocarboxylic acids, particularly acrylic and methacrylic acids, have been recognized as effective toxicants for numerous applications, including antifouling paints. The use of these polymers for protecting a variety of materials against the growth of harmful organisms is disclosed in U.S. Pat. No. 3,167,473.
Monomeric precursors of the aforementioned polymers are prepared by reacting an ethylenically unsaturated acid, such as acrylic acid, or a suitable derivative thereof, such as the corresponding acid anhydride, with a triorganotin hydroxide or a bis(triorganotin)oxide. The water formed as a by-product of the reaction is conventionally removed by distillation which is conducted under either atmospheric or reduced pressure. The reaction of an acid with a triorganotin hydroxide can be expressed by the following equation: ##STR1##
In the foregoing equation R.sup.1 represents a hydrocarbon radical containing between 1 and 20 carbon atoms and R.sup.2 represents an ethylenically unsaturated hydrocarbon radical.
The reaction mixture usually includes an inert liquid diluent such as an aromatic hydrocarbon, which forms an azeotropic mixture with water. The acid and triorganotin compound are usually heated to the boiling point of the reaction mixture and a distillation apparatus is employed to remove the water together with a portion of the hydrocarbon diluent. In addition to facilitating removal of the relatively small amount of water formed during the reaction, the diluent lowers the concentration of unsaturated acid and the triorganotin derivative thereof, thereby reducing the likelihood of a spontaneous polymerization. This type of polymerization is undesirable in those instances when the organotin derivative is to be subsequently reacted with other ethylenically unsaturated compounds to form copolymers such as those disclosed in U.S. Pat. No. 3,167,473.
The distillation of hydrocarbon diluent and water is often conducted under reduced pressure to minimize heating of the reaction mixture.
The use of an organic diluent and distillation to remove the diluent and by-product water may be satisfactory when the total volume of reagents and diluent does not exceed about 500 c.c. As the volume of the reaction mixture increases, it becomes more difficult to evenly distribute heat from the walls of the reactor throughout the reaction mixture. Localized overheating may occur, particularly in areas adjacent to that portion of the reaction vessel where heat is being applied. The heat input required to maintain a distillation wherein the vapor phase remains at ambient temperature is significant. If the heat is not rapidly dissipated within the reaction mixture, the resultant localized overheating could initiate a spontaneous polymerization.
An objective of this invention is to provide a method for preparing relatively large amounts of triorganotin carboxylates derived from ethylenically unsaturated acids with or without any organic diluent and in the absence of significant polymer formation.
It has now been found that this objective can be realized by replacing the conventional distillation step for the removal of water by the use of certain chemicals which will effectively remove the water from the liquid phase of the reaction mixture.